Even more North Carolina households than previously thought could be exposed to Chromium 6 in their drinking water, some of them at unsafe levels. However, the source of the contamination is not Duke Energy’s leaking coal ash ponds, but rather ancient volcanic rock leaching into aquifers.

Avner Vengosh, a Duke University professor of geochemistry and water quality at Duke University’s Nicholas School of the Environment, released the results of a new study today.

Of the 376 wells researchers sampled, 90 percent had detectable levels of Chromium 6, also known as hexavalent chromium, which can cause cancer. Some wells were close to coal ash ponds; others were far away.

By using tracers and analyzing the geochemical fingerprint of contaminants, Vengosh and his team could follow the Chromium 6 back to its source. Think of it as the contaminants’ DNA.

“Our analysis showed that groundwater samples with high levels of hexavalent chromium have very different geochemical fingerprints than what we see in groundwater contaminated from leaking coal ash ponds,” Vengosh said in an announcement by the Nicholas School.

Duke Energy’s coal ash ponds, though, are not benign. Vengosh said that arsenic and selenium in well water near those ponds does come from coal ash. “The impact of leaking coal ash ponds on water resources is still a major environmental issue,” Vengosh said.

While the study results could be a positive development for Duke Energy, it’s bad news for the thousands of private well owners — nearly a third of North Carolinians — who may be exposed to Chromium 6 from natural sources.

“This doesn’t mean it poses less of a threat,” Vengosh said. “If anything, because the contamination stems from water-rock interactions that are common across the Piedmont region, people in a much larger geographic area may be at risk.”

Chromium 6 is also present in many public water systems both in North Carolina and nationwide. The NC Department of Environmental Quality and the Department of Health and Human Services — with involvement from the governor’s office — used that fact to assure some well owners near coal ash ponds that their water posed no threat under the Safe Drinking Water Act.

This was controversial because there is no federal drinking water standard for Chromium 6. Under the SDWA, the levels of total chromium, which combines two types, is capped at 100 parts per billion.

State toxicologist Ken Rudo and state epidemiologist Megan Davies were both concerned that by invoking the Safe Drinking Water Act, the state was misleading well owners and downplaying the health risk.

Nor does the federal standard apply to groundwater or well water near coal ash impoundments. Plus, the science supporting that standard is 25 years old.

Vengesh’s research could change environmental and health policy, although since the findings were just released today, it’s too early to know.

For example, under state legislation passed in 2006, new wells must be tested for contaminants before they can be used. However, existing wells have no such requirement. Private well owners can have their wells tested, but it is not incumbent upon state regulators to fix the problem.

Now that science has further reinforced the theory that Chromium 6 is more widespread, legislation could introduced to test more private wells. In fact, DHHS issued 50 to 70 health risk evaluations for Chromium 6 in wells that were not near ash basins.

Additional testing would likely be expensive and require a significant appropriation. And the state would likely have to consider how to accurately convey any health risks to well owners, who would likely have to pay for filtration or other remedies themselves.

The findings could also prompt a call for the state to impose more stringent drinking water and groundwater standards, similar to that of California. It’s the only state to set a maximum level for Chromium 6 in drinking water — 10 parts per billion.

Clean Water for North Carolina reiterated several of the study findings, including that contaminants from coal ash sites have polluted nearby groundwater. “The findings also do not make the excavation and safe storage of coal ash and provision of clean drinking water sources to neighboring communities any less urgent.”